Thank you for modifying that first line.
I think that the best argument for this position is if you are reading αὐτῶν as a person object of ἀποκρύπτειν. “to hide that σοφία from them.” But you and Hylander refer to “their πλημμελεια, their mistaken belief,” so it is hard to tell what exactly you think the parse for this is.
But taking it either way, the statement as you translate it does not make any sense here. Socrates’ argument is that the highest form of σοφία is hidden from all mankind, full stop, and the best that one can do is, like Socrates, recognize one’s own ignorance. It’s his entire point really. This highest σοφία is not hidden by any particular πλημμέλεια. Rather, it’s impossible for all. Neither people who make the error, nor Socrates who does not, has this σοφία.
Your rephrase though, would be a possible argument for Socrates to make here: “their sofia in one area effectively blinded them to their lack of sofia in the most important things, τα μεγιστα.” But that paraphrase (if I can even call it that) goes well beyond “αὐτῶν αὕτη ἡ πλημμέλεια ἐκείνην τὴν σοφίαν ἀποκρύπτειν”. It’s just not signaled or implied by the Greek here, and does some violence to what is expressed.
In opposition to you, I think, Burnet does not read αποκρύπτειν as “to hide X from Y” here, but just “to hide” or “occultare”. “To throw into the shade” is his gloss. For him the τὰ μέγιστα is political knowledge. The χειροτέχναι – like every craftsman I’ve ever talked to – think that their local expertise means that they possess the knowledge to rule Athens. Helm seems to follow Burnet, glossing as “the most important things,” saying that it is particularly ethics and politics.
As far as your claim that the χειροτέχναι episode simply exists as a repeat of the ποιηταί and the δημιουργοί, I think that this is the least supportable claim of all. The three episodes are not mere repetitions, but a progression. The δημιουργοί make the simple error, thinking that they know something when they know nothing. The ποιηταί, in contrast, have access to some sort of more-than-human knowledge, but they are conduits rather than possessors of it. And the χειροτέχναι, for whom Socrates has the most narrative sympathy, have a real sort of knowledge, one which Socrates admires but does not possess, yet this knowledge is obscured, or shadowed, by their error.
Again, it’s hard to see how you and Hylander are taking αὐτῶν, but I believe that it actually needs to be understood as a possessive referring to αὕτη ἡ πλημμέλεια. It’s fronted for emphasis which signals that this is the specific error of the χειροτέχναι, as separate from the ποιηταί or the δημιουργοί. You two just need to dismiss this added σοφία that is so unnecessarily extracted from σοφώτατος as a referent and the section should be clear.